Aqueous dispersion materials containing a functional substance have conventionally been known widely as functional materials, such as agricultural chemicals such as herbicides or insecticides, pharmaceuticals such as antitumor agents, antiallergic agents or antiphlogistics, and coloring materials such as ink or toner containing a coloring agent. In particular, coloring materials are dissolved or dispersed, so as to prepare an ink composition or toner composition. “Journal of Polymer Science Part A, Polymer Chemistry” Vol. 27, pp. 3303 to 3314, 1989 discloses a preferred use of various polymer materials, in which vinyl polymers such as styryl, acryl or methacryl polymers are used. With regard to a coloring material composition comprising a solvent or water as a base material, an attempt has generally been made that a polymer material preferably comprising an ionic functional group is used, so as to improve dispersibility of coloring materials such as pigments. In addition, using such toner compositions or ink compositions, digital printing techniques have been highly developed in recent years. Electrophotography and ink-jet technique are representative examples of such digital printing techniques, and in these years, the presence of such techniques have been increasingly enhanced as image formation techniques applied both in office and home.
Among others, the ink-jet technique is a direct recording method characterized in that it is compact in scale, resulting in low power consumption. In addition, image quality is being rapidly improved by miniaturization of nozzles or the like. Examples of such ink-jet techniques include a method comprising heating an ink supplied from an ink tank with a heater in a nozzle so as to evaporate the ink and form an ink bubble, and then ejecting the ink bubble to form an image oh a recording medium. Another example is a method of vibrating piezo elements to elect an ink from a nozzle. Since an aqueous dye solution has been commonly used as ink used in these methods, there have been some cases where smearing has been occurred, or a phenomenon called feathering has been appeared in the fiber direction of paper at a recording area on a recording medium, when different colors were overlaid. U.S. Pat. No. 5,085,698 describes that the use of pigment dispersion ink has been studied to improve the above problems. However, it is still desired that many other improvements have been made for such ink.